In the field of the optical networks, an optical add-drop multiplexer (OADM) that adds or drops optical signals of a given wavelength, or a wavelength cross connect (WXC) which is also called an optical hub has come into practical use, resulting in optical networks having a complicated topology such as an interconnection of rings and a mesh. There is a growing need for optimized design, for example, optical transmission design and device layout, in such a complicated network (see for example, International Publication Pamphlet No. 2005/006604 and Japanese Laid-Open Patent Publication No. 2005-166698).
For example, a wavelength dispersion compensation design technique of designing the layout of dispersion compensation modules (DCM) is known. According to the wavelength dispersion compensation design technique, for instance, nodes (sites) in an optical network are grouped into segments, and transmission through any path (for example, a wavelength path) that connects two nodes in a segment is possible.
However, according to the technique above, for instance, with regard to paths that bridge segments, a path having fewer spans than a path capable of transmission may become incapable of transmission, resulting in an a strange design. Such a design is difficult for a user to understand and the user does not easily accept the design.